Studies for this year have shown that circulating monocytes penetrate the intima at pre-lesion stages in hypercholesterolemic swine, become phagocytic and apparently constitute the major source of foam cells in fatty lesions. There is evidence to indicate that these foam cells migrate back into the blood stream once they are lipid-laden. This monocyte system may therefore provide an effective lipid clearance system in early atherogenesis. These findings occur in areas of Evans blue uptake which are predisposed to early lesion development. Other studies indicate that such areas have an altered GAG content and distribution, and that hypercholesterolemia alters GAG content. Such areas also accumulate intravenously-injected ferritin in larger amounts, and preliminary data would suggest a greater number of endothelial pinocytotic vesicles transporting ferritin in these areas.